Fatty acid soaps have been widely employed and known for centuries as general all purpose detergents. However, fatty acid soaps have various shortcomings in that they react with calcium and magnesium ions to form water-insoluble salts when used in hard water. These water-insoluble salts, known as lime soaps, form curds which are commonly observed in the bath or basin where they rise to the surface as scum and adhere as an unsightly ring to the bath or basin. The lime soaps may also leave a film or a feeling of tightness on the skin after washing in hard water with fatty acid soaps.
To reduce soap scum, lime-soap dispersants are commonly added to fatty acid soaps and actually prevent the formation of curds by keeping the lime soaps finely divided and suspended in hard water. Use of these lime soaps dispersing agents in soap have been disclosed in U.S. Pat. Nos. 2,983,684, 3,850,834, and 3,640, 882. Examples of dispersing agents combined with soap to decrease curd formation are sulfosuccinate half esters prepared from ethoxylated alcohols, alkyl phenoloxy alkylene ether sulfates, and surfactants. See Weil et al Soap-Based & Detergent Formulations: xx. The Physical and Chemical Nature of Lime Soap Dispensions, presented at the AOCS meeting (Sept. 1975).
Although use of a soap combined with a lime soap dispersant may eliminate lime curd, several problems do arise with this combination. First of all, many mild synthetic surfactants formulated with soap exhibit poor lather performance compared to soap bars which are rich in coconut soap and are superfatted. Secondly, use of anionic surfactants can yield a high lather volume, but are harsh on the skin. Thirdly, skin roughness or cutaneous tightness has been shown to correlate to the ability of different surfactants to bind to the skin. Imokawa et al Nahihi Kaishi 86 473-481 (1976); J. Soc. Cosmet Chem. 85 147-156 (1984).
To eliminate the harshness problem caused by the use of a synthetic surfactant in soap, U.S. Pat. No. 4,673,525 and GB Pat. No. 2,175,005, disclose adding to the surfactant and soap combination, polymeric mildness skin feel aids and moisturizers. These additives comprise between 10.1-35% of the toilet bar. Although skin roughness is eliminated, it is done so through additional additives that may increase production costs and leave the skin with a greasy filmy feeling due to the moisturizers.
On the other hand, harshness was not a consideration in U.S. Pat. No. 4,397,754 disclosing a personal cleaning product. The detergent composition utilized in said patent has the ability to lather in both hot and cold water. A non-ionic alcohol ethoxylate (90-10% by weight) and a fatty acid soap (10-90% by weight) were impregnated on a polyurethane foam for washing purposes; no mildness additives were disclosed in said patent. Therefore use of this personal cleaning product may leave the skin feeling rough.
Thus, there is a need in the art to produce a mild primarily soap based complexion soap bar that can be used in hard water but prevents cutaneous roughness and tightness while exhibiting a high lather performance without additional mildness additives that may leave the skin feeling greasy.